The present invention relates to control systems for an internal combustion engine, and more particularly to an airflow estimator for internal combustion engines with displacement on demand.
xe2x80x9cAir-leadxe2x80x9d control systems for internal combustion engines estimate an inlet airflow rate of the engine to control the air/fuel ratio. If fuel is controlled to the individual cylinders, such as through conventional port fuel injection, the airflow rate for each of the cylinders is also estimated. The fuel flow rate delivered by the fuel injectors is adjusted based on the estimated airflow to provide the desired air/fuel ratio, such as a stoichiometric air/fuel ratio.
When operating at the stoichiometric air/fuel ratio, the catalytic converter more efficiently reduces undesirable exhaust gas constituents. Minor deviations from the stoichiometric air/fuel ratio significantly degrade the efficiency of the catalytic converter, which increases emissions.
The precision of air-lead control systems is limited by the accuracy of the inlet airflow rate estimates. When engine inlet air dynamics are in steady state, a conventional mass airflow meter that is located in the engine inlet airflow path provides an accurate estimate. Steady state operation occurs when the air pressure in the engine intake manifold is substantially constant over a sufficient time period. When significant manifold filling or depletion are absent, the mass airflow meter accurately estimates cylinder inlet airflow rate.
The mass airflow meter does not accurately characterize cylinder inlet airflow rate under transient conditions due to significant time constants that are associated with manifold filling, manifold depletion, and/or mass airflow meter lag. Transient conditions can arise in a variety of circumstances during engine operation. For example, transient conditions arise when displacement on demand engines increase or decrease the number of operating cylinders. In addition, substantial changes in engine inlet throttle position (TPOS) or other conditions that perturb engine manifold absolute pressure (MAP) also create transient conditions. Transient conditions inject errors in the mass airflow meter estimate. In addition to increasing emissions, the failure to achieve a stoichiometric air/fuel ratio adversely impacts vehicle drivability and torque output.
Airflow estimation systems developed by the assignee of the present invention are disclosed in U.S. Pat. Nos. 5,270,935, 5,423,208, and 5,465,617, which are hereby incorporated by reference. The airflow estimation systems disclosed in these patents do not adequately estimate inlet airflow for displacement on demand engines such as cylinder deactivation engines. These airflow estimation systems do not correctly estimate the cylinder inlet airflow when the engine is running on less than all of the cylinders. In addition, these airflow estimation systems do not accurately estimate airflow during cylinder activation and deactivation transitions.
An airflow estimation method and apparatus according to the present invention for a displacement on demand engine estimates cylinder air charge. A model is provided that estimates cylinder air charge. The model includes a history vector of inputs and states that are updated when a cylinder firing interrupt occurs. An operating mode of the engine is determined. Based on the operating mode, model parameters and model inputs are selected. The cylinder air charge is estimated.
In other features of the invention, the model is capable of predicting cylinder air charge for future cylinder firing interrupts. The operating mode of the engine includes half and full cylinder modes. The model inputs for the half cylinder mode are taken over a crank angle period twice as long as the full cylinder mode. The estimating step is performed during the half cylinder mode only when an active cylinder firing interrupt occurs.
In yet other features, when switching from full cylinder mode to half cylinder mode, blending of half and full cylinder model inputs is performed for a first calibrated time. When switching from half cylinder mode to full cylinder mode, blending of half and full cylinder model inputs is performed for a second calibrated time.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.